Site type classification for the shelter-forest ecological project along the Tarim Desert Highway

Site types of the afforestation region of the shelter-forest ecological project along the Tarim Desert Highway were classified based on the natural conditions and windblown sand damages. The extremely severe environment, the irrigation with saline water, and large-scale linear project makes this classification of site types most unique and significant. It adopted a three-level classification system integrating the dominant factors and restrictive factors in regard to their impacts on plant survival and growth as well as on the protective property. Six site type districts were classified based on the medium-scale geomorphic unit, the windblown sand damages, and the major production facilities; 21 site type groups were obtained according to the small-scale geomorphic type, terrain, and wind regime; 36 site types were further classified based on the salt contents of the underground water and soil types. Especially, in this study, spatial distribution of the six site type districts along the desert highway is continuous, which is unique and different from that of most other classifications. In addition, the salt-stress tolerance threshold of the main afforestation plant species to underground water have been set to 8 g/L and 15 g/L according to selective breeding tests and the salinity spatial distribution of the underground water. Thus, the underground water with salinity lower than 8 g/L is defined as light saline water in this area.